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  1. THE ARCTIC THREAD This is a brand new thread for everything to do with the Arctic as well as Antarctica. I hope that many forum members will contribute on here. I have been a keen weather enthusiast for well over 50 years and have developed widespread interests in many meteorological topics. I have always been particularly fascinated by the Arctic and how it interacts with global climate patterns. We have seen a worrying decline in Arctic sea ice extent during the last 30 years and the Arctic has become the centre of the global warming and climate change debate. Whilst this is undoubtedly highly influenced by human activities, there are also some longer term natural changes in play too. I always like to examine the facts and not be overly influenced by exaggerated reports at either end of the debate which has become highly political. This thread will cover a wide range of topics including: Arctic sea ice extent - current and historic levels, rates of change, ice melt and refreezing, ice loss, ice age (new and older ice), comparisons and analysis with regular updates. Antarctica sea ice extent - as above plus features on the ice shelves and the differences between the two polar regions, facts and figures. Arctic and Antarticaa Sea surface temperatures - current, historic, trends, anomalies, reasons for changes. Arctic and Antarctica air temperatures, monitoring at certain sites, records, changes, data sets. Northern Hemisphere snow cover - seasonal changes, yearly and longer term variations, influences on regional climate and weather patterns. The Greenland ice cap - long term and current research, measurements, trends, rates of change. Glaciers - facts and figures, which ones are declining, which ones are growing, rates of change, global net ice loss. The Polar Vortex - how does this influence the Arctic climate? How does Arctic warming and ice loss influence the polar vortex? North America climate focus - how and when changes in the Arctic impact on the higher and middle latitudes (I often produce European and UK focused reports on a UK weather forum). Historic climates, research into Ice Ages and inter-glacial warmer periods. Climate change and its influence on the Arctic and Antarctica, how much, how fast, why? Global Warming Debate - assessing the extent of human impacts, separating the facts from the fiction, taking a "balanced" approach. Sudden Stratospheric Warming - impacts on the Arctic, what happens, how fast, why? The Arctic oscillation and the Antarctic oscillation - current, forecast, anomalies and historic values, links to weather patterns. Arctic and Antarctica news and events - special features and reports with comments and analysis (eg: the recent clouds of smoke covering the Arctic from vast Siberian forest fires) I will add to this list as this thread evolves. In general I would like this thread to appeal to as wide an audience as possible. I'm a great believer in keeping things simple and explaining topics in plain English. I regularly post on the "Teleconnections" thread and some of the more complex subjects such as how does the Arctic ice loss teleconnecton interact with other teleconnections may be more suitable for that thread (or perhaps both threads). There are already some excellent papers and video presentations relating to the Arctic in the "Teleconnections Research Portal" and we will be adding a lot more as winter approaches. Some of these papers may be reviewed on this thread especially when they relate to a particular post. List of Useful Links to Arctic and Antarctica Sites, Data, Facts, Charts etc: This list will gradually evolve in line with the thread (so work in progress). If you have a link that you feel is relevant, please draw this to my attentions by "replying to topic" or with a "personal message". Here's a direct link to the Teleconnections Research Portal - we have placed many Arctic related papers and presentations in there with many more being added during the coming months. National Snow and Ice Data Center (NSIDC): - daily ice cover updates and monthly reports. Arctic Sea Ice graphs: - this huge site with many sub links provides any extraordinary amount current and historic ice data, charts and maps. NOAA National Weather Centre Environmental Modelling Centre Global Sea Surface Temperatures and Anomaly Maps: (click on the map for any region). NOAA Snow Cover Maps: - current, historic and animated snow cover maps for Northern Hemisphere, North America and Eurasia. NCEP 2m Surface Temperature Anomalies by region: - includes forecast, current and past charts with extensive Arctic and Antarctica coverage. NASA WorldView Satellite Imagery: - with many options and tools to create your own world or regional images. Polar Science Center: - packed with Arctic news, research, data and links to conferences and papers (some of these are already in the Research Portal and more to add). Zachary (Zach) Labe: - a Ph.D. student, Dept of Earth System Science, University of California; fascinating Arctic research, reports, data, charts and links to papers. Climate Reanalyzer: - for current weather data and analysis (northern hemisphere). many more to follow during the next few weeks Arctic Ocean Regional Map Showing All the Seas: I show an Arctic map (below) to identify the locations of all the seas that make up the Arctic Ocean so that we can comment more meaningfully on the local variations in our posts on this thread. Antarctica Map: I will kick things off with a series of short posts to give a flavour of what might follow. I'll do one on the current Arctic sea ice extent later today and two more tomorrow on Arctic sea surface temperatures and Northern Hemisphere snow cover. If I have time, I will do another one on Arctic air temperatures and also show that report on the Arctic ash cloud spreading from those Siberian forest fires. When I return from a business trip, I'll add several more posts later next week. I would really like to see other forum members getting involved on here with posts and comments and I hope that we can get some debates going too. David
  2. The urgency of Arctic change Authors: James Overland, Edward Dunlea, Jason E.Box, Robert Corell, Martin Forsius, Vladimir Kattsov, Morten Skovg ård Olsen, Janet Pawlak, Lars-OttoReiersen and MuyinWang Published: November 27th, 2018 Abstract: This article provides a synthesis of the latest observational trends and projections for the future of the Arctic. First, the Arctic is already changing rapidly as a result of climate change. Contemporary warm Arctic temperatures and large sea ice deficits (75% volume loss) demonstrate climate states outside of previous experience. Modeled changes of the Arctic cryosphere demonstrate that even limiting global temperature increases to near 2 °C will leave the Arctic a much different environment by mid-century with less snow and sea ice, melted permafrost, altered ecosystems, and a projected annual mean Arctic temperature increase of +4 °C. Second, even under ambitious emission reduction scenarios, high-latitude land ice melt, including Greenland, are foreseen to continue due to internal lags, leading to accelerating global sea level rise throughout the century. Third, future Arctic changes may in turn impact lower latitudes through tundra greenhouse gas release and shifts in ocean and atmospheric circulation. Arctic-specific radiative and heat storage feedbacks may become an obstacle to achieving a stabilized global climate. In light of these trends, the precautionary principle calls for early adaptation and mitigation actions. Link to full paper (on the "ScienceDirect" website): Link to pdf early manuscript version of the paper:
  3. An observational analysis: Tropical relative to Arctic influence on mid-latitude weather in the era of Arctic amplification Author: Dr. Judah Cohen Published: May 2016 Abstract: The tropics, in general, and El Niño/Southern Oscillation (ENSO) in particular are almost exclusively relied upon for seasonal forecasting. Much less considered and certainly more controversial is the idea that Arctic variability is influencing mid-latitude weather. However, since the late 1980s and early 1990s,the Arctic has undergone the most rapid warming observed globally, referred to as Arctic amplification (AA), which has coincided with an observed increase in extreme weather. Analysis of observed trends in hemispheric circulation over the period of AA more closely resembles variability associated with Arctic boundary forcings than with tropical forcing. Furthermore, analysis of intra seasonal temperature variability shows that the cooling in mid-latitude winter temperatures has been accompanied by an increase in temperature variability and not a decrease, popularly referred to as “weather whiplash.” Link to full paper:
  4. Narrowing of the ITCZ in a warming climate: Physical mechanisms First published: 22 October 2016 Authors: Michael P. Byrne and Tapio Schneider First Published: October 22nd, 2016 Published on line: June 14th, 2016 Abstract: The Intertropical Convergence Zone (ITCZ) narrows in response to global warming in both observations and climate models. However, a physical understanding of this narrowing is lacking. Here we show that the narrowing of the ITCZ in simulations of future climate is related to changes in the moist static energy (MSE) budget. MSE advection by the mean circulation and MSE divergence by transient eddies tend to narrow the ITCZ, while changes in net energy input to the atmosphere and the gross moist stability tend to widen the ITCZ. The narrowing tendency arises because the meridional MSE gradient strengthens with warming, whereas the largest widening tendency is due to increasing shortwave heating of the atmosphere. The magnitude of the ITCZ narrowing depends strongly on the gross moist stability and clouds, emphasizing the need to better understand these fundamental processes in the tropical atmosphere. Link to Paper:
  5. Energetic Constraints on the Width of the Intertropical Convergence Zone Authors: Michael P. Byrne and Tapio Schneider First Published: February 9th, 2016 Published on line: June 14th, 2016 Abstract: The intertropical convergence zone (ITCZ) has been the focus of considerable research in recent years, with much of this work concerned with how the latitude of maximum tropical precipitation responds to natural climate variability and to radiative forcing. The width of the ITCZ, however, has received little attention despite its importance for regional climate and for understanding the general circulation of the atmosphere. This paper investigates the ITCZ width in simulations with an idealized general circulation model over a wide range of climates. The ITCZ, defined as the tropical region where there is time-mean ascent, displays rich behavior as the climate varies, widening with warming in cool climates, narrowing in temperate climates, and maintaining a relatively constant width in hot climates. The mass and energy budgets of the Hadley circulation are used to derive expressions for the area of the ITCZ relative to the area of the neighboring descent region, and for the sensitivity of the ITCZ area to changes in climate. The ITCZ width depends primarily on four quantities: the net energy input to the tropical atmosphere, the advection of moist static energy by the Hadley circulation, the transport of moist static energy by transient eddies, and the gross moist stability. Different processes are important for the ITCZ width in different climates, with changes in gross moist stability generally having a weak influence relative to the other processes. The results are likely to be useful for analyzing the ITCZ width in complex climate models and for understanding past and future climate change in the tropics. Link to Paper:
  6. Fast and Slow Components of the Extratropical Atmospheric Circulation Response to CO2 Forcing Authors: Paulo Ceppi, Giuseppe Zappa, Theodore G. Shepherd and Jonathan M. Gregory First Published: September 15th, 2017 Published on line: January 19th, 2018 Abstract: Poleward shifts of the extratropical atmospheric circulation are a common response to CO2 forcing in global climate models (GCMs), but little is known about the time dependence of this response. Here it is shown that in coupled climate models, the long-term evolution of sea surface temperatures (SSTs) induces two distinct time scales of circulation response to steplike CO2 forcing. In most GCMs from phase 5 of the Coupled Model Intercomparison Project as well as in the multimodel mean, all of the poleward shift of the midlatitude jets and Hadley cell edge occurs in a fast response within 5–10 years of the forcing, during which less than half of the expected equilibrium warming is realized. Compared with this fast response, the slow response over subsequent decades to centuries features stronger polar amplification (especially in the Antarctic), enhanced warming in the Southern Ocean, an El Niño–like pattern of tropical Pacific warming, and weaker land–sea contrast. Atmosphere-only GCM experiments demonstrate that the SST evolution drives the difference between the fast and slow circulation responses, although the direct radiative effect of CO2 also contributes to the fast response. It is further shown that the fast and slow responses determine the long-term evolution of the circulation response to warming in the representative concentration pathway 4.5 (RCP4.5) scenario. The results imply that shifts in midlatitude circulation generally scale with the radiative forcing, rather than with global-mean temperature change. A corollary is that time slices taken from a transient simulation at a given level of warming will considerably overestimate the extratropical circulation response in a stabilized climate. Link to Paper:
  7. Response of the Zonal Mean Atmospheric Circulation to El Niño versus Global Warming Authors: Jian Lu, Gang Chen and Dargan M. W. Frierson First Published: March 11th, 2008 Published on line: November 15th, 2008 Abstract: The change in the zonal mean atmospheric circulation under global warming is studied in comparison with the response to El Niño forcing, by examining the model simulations conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In contrast to the strengthening and contraction of the Hadley cell and the equatorward shift of the tropospheric zonal jets in response to El Niño, the Hadley cell weakens and expands poleward, and the jets move poleward in a warmed climate, despite the projected “El Niño–like” enhanced warming over the equatorial central and eastern Pacific. The hydrological impacts of global warming also exhibit distinct patterns over the subtropics and midlatitudes in comparison to the El Niño. Two feasible mechanisms are proposed for the zonal mean circulation response to global warming: 1) The increase in static stability of the subtropical and midlatitude troposphere, a robust result of the quasi-moist adiabatic adjustment to the surface warming, may stabilize the baroclinic eddy growth on the equatorward side of the storm tracks and push the eddy activity and the associated eddy-driven wind and subsidence poleward, leading to the poleward expansion of the Hadley cell and the shift of midlatitude jets; 2) the strengthening of the midlatitude wind at the upper troposphere and lower stratosphere, arguably a consequence of increases in the meridional temperature gradient near the tropopause level due to the tropospheric warming and tropopause slope, may increase the eastward propagation of the eddies emanating from the midlatitudes, and thus the subtropical region of wave breaking displaces poleward together with the eddy-driven circulation. Both mechanisms are somewhat, if not completely, distinct from those in response to the El Niño condition. Link to full paper: Credit goes to Eric @Webberweather for finding this presentation - thank you.
  8. Relationship between Tropical Pacific SST and global atmospheric angular momentum in coupled models Authors: Huei−Ping Huang, Matthew Newman, Richard Seager, Yochanan Kushnir and Participating CMIP2+ Modeling Groups First Published: January 2004 Abstract: The sensitivity parameter S1 = ∆AAM/∆SST, where ∆AAM and ∆SST represent the anomalies of global atmospheric angular momentum (AAM) and tropical Pacific sea surface temperature (SST) in the NINO3.4 region, is compared for the CMIP2+ coupled models. The parameter quantifies the strength of atmospheric zonal mean zonal wind response to SST anomaly in the equatorial Pacific, an important process for the climate system. Although the simulated ∆AAM and ∆SST are found to exhibit great disparity, their ratios agree better among the coupled models (and with observation) with no significant outliers. This indicates that the processes that connect the AAM anomaly to tropical SST anomaly are not sensitive to the base SST and the detail of convective heating and are relatively easy to reproduce by the coupled models. Through this robust ∆SST−∆AAM relationship, the model bias in tropical Pacific SST manifests itself in the bias in atmospheric angular momentum. The value of S1 for an atmospheric model forced by observed SST is close to that for a coupled model with a similar atmospheric component, suggesting that the ∆SST− ∆AAM relationship is dominated by a one−way influence of the former forcing the latter. The physical basis for the ∆SST−∆AAM relationship is explored using a statistical equilibrium argument that links ∆SST to the anomaly of tropical tropospheric temperature. The resulting meridional gradient of tropospheric temperature is then linked to the change in zonal wind in the subtropical jets, the main contributor to ∆AAM, by thermal wind balance. Link to Paper: Credit goes to Tom @Isotherm for finding this paper - thank you.
  9. Global Warming and ENSO – A “Helter-Skelter” Atmosphere Authors: Daphne Thompson (for WDT) Published: 11th December, 2017 Abstract: (None but I extracted this from the text): The purpose of this article is to make an effort to illustrate circulation impacts due to climate change, and give some high-level observational evidence of a La Niña-like response due to global warming, including at present. From another perspective, the ongoing El Niño could be contributing to La Niña aspects of the current atmospheric circulation given that it may be amplifying the present increase in the global mean temperature. Emphasis is then placed on the relevancy of climate change to subseasonal forecasting, including the present 16-30 day outlooks issued by WDT. The “global warming-La Niña” connection has been gaining some recognition in a few very recent publications in the refereed literature, as well as in on-line blogs written by well-respected scientists. The reader is encouraged to do a search. No attempt will be made to get into the complicated issues of the causes of climate change (including global warming) other than described above Link to full paper: Credit goes to Tams @Tamara for finding this paper - thank you.
  10. Why CO2 cools the middle atmosphere – a consolidating model perspective Authors: Helge F. Goessling and Sebastian Bathiany Published: 29th August, 2016 Abstract: Complex models of the atmosphere show that increased carbon dioxide (CO2) concentrations, while warming the surface and troposphere, lead to lower temperatures in the stratosphere and mesosphere. This cooling, which is often referred to as “stratospheric cooling”, is evident also in observations and considered to be one of the fingerprints of anthropogenic global warming. Although the responsible mechanisms have been identified, they have mostly been discussed heuristically, incompletely, or in combination with other effects such as ozone depletion, leaving the subject prone to misconceptions. Here we use a one-dimensional window-grey radiation model of the atmosphere to illustrate the physical essence of the mechanisms by which CO2 cools the stratosphere and mesosphere: (i) the blocking effect, associated with a cooling due to the fact that CO2 absorbs radiation at wavelengths where the atmosphere is already relatively opaque, and (ii) the indirect solar effect, associated with a cooling in places where an additional (solar) heating term is present (which on Earth is particularly the case in the upper parts of the ozone layer). By contrast, in the grey model without solar heating within the atmosphere, the cooling aloft is only a transient blocking phenomenon that is completely compensated as the surface attains its warmer equilibrium. Moreover, we quantify the relative contribution of these effects by simulating the response to an abrupt increase in CO2 (and chlorofluorocarbon) concentrations with an atmospheric general circulation model. We find that the two permanent effects contribute roughly equally to the CO2-induced cooling, with the indirect solar effect dominating around the stratopause and the blocking effect dominating otherwise. Link to full paper: Credit goes to Eric @Webberweather for finding this paper - thank you.
  11. Seasonal and Regional Manifestation of Arctic Sea Ice Loss Authors: Ingrid H. Onarheim, Tor Eldevik, Lars H. Smedsrud, Julienne C. Stroeve Published: May2018 Abstract: The Arctic Ocean is currently on a fast track toward seasonally ice-free conditions. Although most attention has been on the accelerating summer sea ice decline, large changes are also occurring in winter. This study assesses past, present, and possible future change in regional Northern Hemisphere sea ice extent throughout the year by examining sea ice concentration based on observations back to 1950, including the satellite record since 1979. At present, summer sea ice variability and change dominate in the perennial ice-covered Beaufort, Chukchi, East Siberian, Laptev, and Kara Seas, with the East Siberian Sea explaining the largest fraction of September ice loss (22%). Winter variability and change occur in the seasonally ice-covered seas farther south: the Barents Sea, Sea of Okhotsk, Greenland Sea, and Baffin Bay, with the Barents Sea carrying the largest fraction of loss in March (27%). The distinct regions of summer and winter sea ice variability and loss have generally been consistent since 1950, but appear at present to be in transformation as a result of the rapid ice loss in all seasons. As regions become seasonally ice free, future ice loss will be dominated by winter. The Kara Sea appears as the first currently perennial ice-covered sea to become ice free in September. Remaining on currently observed trends, the Arctic shelf seas are estimated to become seasonally ice free in the 2020s, and the seasonally ice-covered seas farther south to become ice free year-round from the 2050s. Link to full paper:
  12. The influence of Arctic amplification on mid-latitude summer circulation Authors: D. Coumou, G. Di Capua, S. Vavrus, L. Wang & S. Wang Published: 20th August 2018 Abstract: Accelerated warming in the Arctic, as compared to the rest of the globe, might have profound impacts on mid-latitude weather. Most studies analyzing Arctic links to mid-latitude weather focused on winter, yet recent summers have seen strong reductions in sea-ice extent and snow cover, a weakened equator-to-pole thermal gradient and associated weakening of the mid-latitude circulation. We review the scientific evidence behind three leading hypotheses on the influence of Arctic changes on mid-latitude summer weather: Weakened storm tracks, shifted jet streams, and amplified quasi-stationary waves. We show that interactions between Arctic teleconnections and other remote and regional feedback processes could lead to more persistent hot-dry extremes in the mid-latitudes. The exact nature of these non-linear interactions is not well quantified but they provide potential high-impact risks for society. Link to full paper:
  13. A real-time Global Warming Index Authors: Dr. K. Haustein, M. R. Allen, P. M. Forster, F. E. L. Otto, D. M. Mitchell, H. D. Matthews and D. J. Frame Published: 13th November, 2017 Abstract: We propose a simple real-time index of global human-induced warming and assess its robustness to uncertainties in climate forcing and short-term climate fluctuations. This index provides improved scientific context for temperature stabilisation targets and has the potential to decrease the volatility of climate policy. We quantify uncertainties arising from temperature observations, climate radiative forcings, internal variability and the model response. Our index and the associated rate of human-induced warming is compatible with a range of other more sophisticated methods to estimate the human contribution to observed global temperature change. Link to full paper:
  14. Effect of AMOC collapse on ENSO in a high resolution general circulation model Authors: Mark S. Williamson, Mat Collins, Sybren S. Drijfhout, Ron Kahana, Jennifer V. Mecking and Timothy M. Lenton Published: 17th June, 2017 Abstract: We look at changes in the El Niño Southern Oscillation (ENSO) in a high-resolution eddy-permitting climate model experiment in which the Atlantic Meridional Circulation (AMOC) is switched off using freshwater hosing. The ENSO mode is shifted eastward and its period becomes longer and more regular when the AMOC is off. The eastward shift can be attributed to an anomalous eastern Ekman transport in the mean equatorial Pacific ocean state. Convergence of this transport deepens the thermocline in the eastern tropical Pacific and increases the temperature anomaly relaxation time, causing increased ENSO period. The anomalous Ekman transport is caused by a surface northerly wind anomaly in response to the meridional sea surface temperature dipole that results from switching the AMOC off. In contrast to a previous study with an earlier version of the model, which showed an increase in ENSO amplitude in an AMOC off experiment, here the amplitude remains the same as in the AMOC on control state. We attribute this difference to variations in the response of decreased stochastic forcing in the different models, which competes with the reduced damping of temperature anomalies. In the new high-resolution model, these effects approximately cancel resulting in no change in amplitude. Link to full paper: complexity.GRL-2018.pdf
  15. Projected SSTs over 21st century: Changes in mean, variability & extremes for large marine ecosystem regions of Northern Oceans Authors: Michael A. Alexander (NOAA), James D. Scott, Kevin D. Friedland, Katherine E. Mills, Janet A. Nye, Andrew J. Pershing and Andrew C. Thomas Published: 26th January, 2018 Abstract: Global climate models were used to assess changes in the mean, variability and extreme sea surface temperatures (SSTs) in northern oceans with a focus on large marine ecosystems (LMEs) adjacent to North America, Europe, and the Arctic Ocean. Results were obtained from 26 models in the Community Model Intercomparison Project Phase 5 (CMIP5) archive and 30 simulations from the National Center for Atmospheric Research Large Ensemble Community Project (CESM-LENS). All of the simulations used the observed greenhouse gas concentrations for 1976–2005 and the RCP8.5 “business as usual” scenario for greenhouse gases through the remainder of the 21st century. In general, differences between models are substantially larger than among the simulations in the CESM-LENS, indicating that the SST changes are more strongly affected by model formulation than internal climate variability. The annual SST trends over 1976–2099 in the 18 LMEs examined here are all positive ranging from 0.05 to 0.5°C decade–1. SST changes by the end of the 21st century are primarily due to a positive shift in the mean with only modest changes in the variability in most LMEs, resulting in a substantial increase in warm extremes and decrease in cold extremes. The shift in the mean is so large that in many regions SSTs during 2070–2099 will always be warmer than the warmest year during 1976–2005. The SST trends are generally stronger in summer than in winter, as greenhouse gas heating is integrated over a much shallower climatological mixed layer depth in summer than in winter, which amplifies the seasonal cycle of SST over the 21stcentury. In the Arctic, the mean SST and its variability increases substantially during summer, when it is ice free, but not during winter when a thin layer of ice reforms and SSTs remain near the freezing point. Link to full paper: Link to a presentation of this paper (slides only): extra slides.pdf
  16. Climate science in the tropics: waves, vortices and PDEs Authors: Boualem Khouider, Andrew J Majda and Samuel N Stechmann Published: 16th November, 2012 Abstract: Clouds in the tropics can organize the circulation on planetary scales and profoundly impact long range seasonal forecasting and climate on the entire globe, yet contemporary operational computer models are often deficient in representing these phenomena. On the other hand, contemporary observations reveal remarkably complex coherent waves and vortices in the tropics interacting across a bewildering range of scales from kilometers to ten thousand kilometers. This paper reviews the interdisciplinary contributions over the last decade through the modus operandi of applied mathematics to these important scientific problems. Novel physical phenomena, new multiscale equations, novel PDEs, and numerical algorithms are presented here with the goal of attracting mathematicians and physicists to this exciting research area. Link to full paper:
  17. Migration of the Lifetime Maximum Intensity of Tropical Cyclones: Relation to Maximum Wind Speeds - Presentation A presentation at the AMS 33rd Conference on “Hurricanes and Tropical Meteorology” held at Ponte Vedra, Florida, USA between 16th and 20th April, 2018 Presenters: Kelsey N. Ellis and S. A. Tennille Presentation Date: 16th April, 2018 Presentation Summary: The climatology of tropical cyclones is an immediate research need, specifically to better understand their long-term patterns and elucidate their future in a changing climate. One important pattern that has recently been detected is the poleward shift of the lifetime maximum intensity (LMI) of tropical cyclones. This study further assessed the recent (1977–2015) spatial changes in the LMI of tropical cyclones, specifically those of tropical storm strength or stronger in the North Atlantic and northern West Pacific basins. Analyses of moving decadal means suggested that LMI locations migrated south in the North Atlantic and north in the West Pacific. In addition to a linear trend, there is a cyclical migration of LMI that is especially apparent in the West Pacific. Relationships between LMI migration and intensity were explored, as well as LMI location relative to landfall. The southerly trend of LMI in the North Atlantic was most prevalent in the strongest storms, resulting in these storms reaching their LMI farther from land. The relationship between intensity and LMI migration in the West Pacific was not as clear, but the most intense storms have been reaching LMI closer to their eventual landfall location. This work adds to those emphasizing the importance of understanding the climatology of the most intense hurricanes and shows there are potential human impacts resulting from any migration of LMI. Link to conference video presentation (10 minutes): Link to full conference agenda:
  18. Review on climate change on the Tibetan Plateau during the last half century Authors: Xingxing Kuang and Jiu Jimmy Jiao Published: 5th April, 2016 Abstract: The Tibetan Plateau (TP) is undergoing significant warming since the 1950s. During the past two decades, extensive research has been conducted to investigate the climate change on the plateau. This review presents an overview of recent progress on climate change on the TP with the aim of providing a comprehensive understanding of changes in climate variables. Long‐term observation data from meteorological stations presented by the published literature were used to show the trends in various climate variables. The TP is overall getting warmer and wetter during the past decades. Temperature is significantly increased, especially since the 1980s. The overall warming rate ranges from 0.16 to 0.67°C decade−1 since the 1950s during different periods. The TP shows a uniform warming trend with the most significant warming in the northern part. Precipitation is slightly increased, and the spatial pattern of changes in precipitation is variable. The annual precipitation is increasing in most areas of the TP. Some subregions are becoming wetter, while some subregions are becoming drier. Pan evaporation, reference evapotranspiration, and potential evapotranspiration have been found to decrease since the 1960s. Actual evapotranspiration is significantly increased since the 1960s. Wind speed and sunshine duration increased up to the 1970s and then decreased significantly afterwards. Relative humidity fluctuated up and down to the end of the 1990s and appeared to decrease afterwards. Vapor pressure deficit shows an overall increasing trend since the 1970s. Causes of changes in the climate variables are presented, and future research directions are recommended. Link to paper (on AGU100 site): Link to full paper (pdf version):
  19. Atlantic Multidecadal Variability as a Modulator of Precipitation Variability in the Southwest United States Authors: Dong Eun Lee and Mingfang Ting Published: 18th June, 2018 Abstract: Two independent atmospheric general circulation models reveal that the positive (negative) phase of Atlantic multidecadal variability (AMV) can reduce (amplify) the variance of the shorter time-scale (e.g., ENSO related) precipitation fluctuations in the United States, especially in the Southwest, as well as decrease (increase) the long-term seasonal mean precipitation for the cold season. The variance is modulated because of changes in 1) dry day frequency and 2) maximum daily rainfall intensity. With positive AMV forcing, the upper-level warming originating from the increased precipitation over the tropical Atlantic Ocean changes the mean vertical thermal structure over the United States continent to a profile less favorable for rain-inducing upward motions. In addition, a northerly low-level dry advection associated with the local overturning leaves less available column moisture for condensation and precipitation. The opposite conditions occur during cold AMV periods. Link to full paper: Please note that the full paper is currently behind an AMS paywall Link to the AMS website:
  20. Projecting North American Climate over the Next 50 Years: Uncertainty due to Internal Variability Authors: Clara Deser and Adam S. Phillips Published: 30th October, 2013 Abstract: This study highlights the relative importance of internally generated versus externally forced climate trends over the next 50 yr (2010–60) at local and regional scales over North America in two global coupled model ensembles. Both ensembles contain large numbers of integrations (17 and 40): each of which is subject to identical anthropogenic radiative forcing (e.g., greenhouse gas increase) but begins from a slightly different initial atmospheric state. Thus, the diversity of projected climate trends within each model ensemble is due solely to intrinsic, unpredictable variability of the climate system. Both model ensembles show that natural climate variability superimposed upon forced climate change will result in a range of possible future trends for surface air temperature and precipitation over the next 50 yr. Precipitation trends are particularly subject to uncertainty as a result of internal variability, with signal-to-noise ratios less than 2. Intrinsic atmospheric circulation variability is mainly responsible for the spread in future climate trends, imparting regional coherence to the internally driven air temperature and precipitation trends. The results underscore the importance of conducting a large number of climate change projections with a given model, as each realization will contain a different superposition of unforced and forced trends. Such initial-condition ensembles are also needed to determine the anthropogenic climate response at local and regional scales and provide a new perspective on how to usefully compare climate change projections across models. Link to full paper:
  21. Key Points & Synthesis - Conference Summary Part 2 Workshop Presentation: Aspen Global Change Institute, Aspen, Colorado Workshop Programme: “Understanding the Causes and Consequences of Polar Amplification” - June 12th -16th, 2017 Presenters: James Screen, Doug Smith and Xiangdong Zhang Presentation Date: 16th June, 2017 Link to full presentation (1 hour 37 minute video): Link to presentation (slides and charts only): synthesis_0.pdf Link to full agenda and presentations:
  22. Key Points & Synthesis - Conference Summary Part 1 Workshop Presentation: Aspen Global Change Institute, Aspen, Colorado Workshop Programme: “Understanding the Causes and Consequences of Polar Amplification” - June 12th -16th, 2017 Presenters: James Screen, Doug Smith and Xiangdong Zhang Presentation Date: 15th June, 2017 Link to full presentation (43 minute video): Link to presentation (slides and charts only): synthesis.pdf Link to full agenda and presentations:
  23. The relative roles of structural uncertainty and internal variability in Antarctic climate change projections Workshop Presentation: Aspen Global Change Institute, Aspen, Colorado Workshop Programme: “Understanding the Causes and Consequences of Polar Amplification” - June 12th -16th, 2017 Presenter: David Schneider Presentation Date: 13th June, 2017 Abstract: None Link to full video presentation (27 minutes): Link to full agenda and presentations:
  24. The Response of the Southern Ocean and Antarctic Sea Ice to Freshwater from Ice Shelves in an Earth System Model Authors: Andrew G. Pauling, Cecelia M. Bitz, J. Smith and Patricia J. Langhorne Published: 5th December, 2015 Abstract: The possibility that recent Antarctic sea ice expansion resulted from an increase in freshwater reaching the Southern Ocean is investigated here. The freshwater flux from ice sheet and ice shelf mass imbalance is largely missing in models that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5). However, on average, precipitation minus evaporation (P − E) reaching the Southern Ocean has increased in CMIP5 models to a present value that is about greater than preindustrial times and 5–22 times larger than estimates of the mass imbalance of Antarctic ice sheets and shelves (119–544 ). Two sets of experiments were conducted from 1980 to 2013 in CESM1(CAM5), one of the CMIP5 models, artificially distributing freshwater either at the ocean surface to mimic iceberg melt or at the ice shelf fronts at depth. An anomalous reduction in vertical advection of heat into the surface mixed layer resulted in sea surface cooling at high southern latitudes and an associated increase in sea ice area. Enhancing the freshwater input by an amount within the range of estimates of the Antarctic mass imbalance did not have any significant effect on either sea ice area magnitude or trend. Freshwater enhancement of raised the total sea ice area by 1 × 106 km2, yet this and even an enhancement of was insufficient to offset the sea ice decline due to anthropogenic forcing for any period of 20 years or longer. Further, the sea ice response was found to be insensitive to the depth of freshwater injection. Link to full paper:
  25. Drivers of Polar Warming - Presentation Workshop Presentation: Aspen Global Change Institute, Aspen, Colorado Workshop Programme: “Understanding the Causes and Consequences of Polar Amplification” - June 12th -16th, 2017 Presenter: John C Fyfe Presentation Date: 13th June, 2017 Abstract: None Link to full video presentation (28 minutes): Link to full agenda and presentations:
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